there is a machined lip part way down from the top to stop the bearing top cup thing coming down too far and the thread would need machining further down because the stem is around 1 inch too long....both top and bottom bearing (retainers?) are smaller in width than the kh125 ones so there is a lot of side to side movement, almost enough for the bearings to come out ( loose bearings )

here's a pic of the gap/spacer i used underneath.

'' If your rear tire has plenty of tread after a ride out, you haven't ridden hard enough ''